The enzymology and regulation of adrenal cortex steroidogenesis will be studied, with particular emphasis on the role of the phospholipid membrane in the control of cytochrome P-450scc-dependent side chain cleavage of cholesterol. Similar studies will be carried out using a kidney cytochrome P-450 which catalyzes the 1alpha-hydroxylation of 25-hydroxyvitamin D. The enzymes adrenodoxin reductase, adrenodoxin, and cytochrome P-450 will be studied using UV-visible absorbence spectrophotometry, stopped flow spectrophotometry, and EPR using spin-labeled phospholipids and cholesterol. Deuterium isotope effects on the cholesterol side-chain cleavage reaction will be investigated and utilized in the study of ACTH effects on activation of adrenal mitochondrial steroidogenesis.